Cyclin D1 Regulation of Nuclear Receptor Function in Breast Cancer

描述(申请人提供)：ErbB2跨膜受体在大约30%的人类肿瘤中过度表达。乳腺靶向ErbB2的过表达足以促进体内乳腺肿瘤的发生。细胞周期蛋白D1基因产物在30-50%的人类乳腺癌中过度表达。细胞周期蛋白D1反义阻断ErbB2诱导的乳腺肿瘤生长，细胞周期蛋白D1-/-小鼠对ErbB2诱导的肿瘤生长具有抵抗作用。PPARGamma核激素受体抑制细胞增殖，促进分化。在几种癌症中发现了PPARGamma的突变、重排和表达变化，这表明PPARGamma可能是一种肿瘤抑制因子。我们发现细胞周期蛋白D1抑制PPARγ的分化功能、反式激活和在培养细胞中的表达。我们已经证明CD1-/-小鼠有反映PPARGamma表达和活性增加的遗传和表型变化，暗示PPARGamma在肿瘤耐药表型中增加。目前的研究将确定细胞周期蛋白D1在体内抑制PPAR伽马信号转导的分子机制。我们将使用乳腺靶向诱导性转基因来确定细胞周期蛋白D1调节PPARGamma功能的分子机制，并确定PPARGamma在ErbB2背景下作为乳腺肿瘤抑制因子的作用。这些研究将会： 1.确定细胞周期蛋白D1抑制PPAR-γ反式激活的机制。将确定细胞周期蛋白D1抑制部分PPAR-γ共激活子的能力。由于PPARGamma是乙酰化的，并且细胞周期蛋白D1HDAC募集结构域控制着PPARGamma的抑制，因此将确定PPARGamma乙酰化在细胞周期蛋白D1抑制中的作用。 2.确定细胞周期蛋白D1抑制PPAR-γ功能和表达的机制。细胞周期蛋白D1阻断PPARGamma诱导的成纤维细胞向脂肪细胞分化。我们将确定调控PPAR-Gamma分化的细胞周期蛋白D1的结构域。将在CD-/-小鼠、Cyclin E敲门子-CD-/-小鼠和孕酮诱导的Cyclin D1反义小鼠中评估Cyclin D1对PPARGamma的调节。PPARGamma和细胞周期蛋白D1的相关表达研究将在良性乳腺疾病和乳腺癌中进行。 3.确定PPAR-γ在ErbB_2诱导的乳腺肿瘤发生中的作用。我们将确定ErbB2和PPARGamma在培养细胞和PPARGamma转基因小鼠中的功能相互作用。可诱导转基因技术的使用将使我们能够在乳腺肿瘤的发生和发展过程中确定PPAR伽马的功能。如果PPARGamma是ErbB2诱导的肿瘤发生的抑制因子，并且PPARGamma的肿瘤抑制功能涉及细胞周期蛋白D1的抑制，这些研究为寻找这种相互作用的激动剂提供了合理的基础，并用于潜在的治疗应用。此外，如果乳腺癌先兆病变中PPARGamma水平降低，良性乳腺疾病中PPARGamma的研究可能提供乳腺癌进展的预测指标。因此，拟议的研究可能具有重要的翻译意义。

DESCRIPTION (provided by applicant): The ErbB2 transmembrane receptor is overexpressed in approximately 30% of human tumors. Mammary gland targeted ErbB2 overexpression is sufficient for mammary tumorigenesis in vivo. The cyclin D1 gene product is overexpressed in 30-50% of human breast cancers. Cyclin D1 anti-sense blocks ErbB2-induced mammary tumor growth and cyclin D1 -/- mice are resistant to ErbB2-induced tumor growth. The PPARgamma nuclear hormone receptor inhibits cellular proliferation and promotes differentiation. Mutations, rearrangements and altered expression of PPARgamma have been identified in several cancers suggesting PPARgamma may function as a tumor suppressor. We have shown cyclin D1 inhibits PPARgamma differentiation function, transactivation and expression in cultured ceils. We have shown CD1 -/- mice have genetic and phenotypic changes reflecting increased PPARgamma expression and activity, implicating increased PPARgamma in the tumor-resistant phenotype. The current studies will determine the molecular mechanisms by which cyclin D1 inhibits PPARgamma signaling in vivo. We will use mammary gland-targeted inducible transgenics to identify the molecular mechanisms by which cyclin D1 regulates PPARgamma function and determine the role of PPARgamma as a mammary gland tumor suppressor in the context of ErbB2. These studies will: 1. Determine the mechanism by which cyclin D1 inhibits PPARgamma transactivation. The ability of cyclin D1 to inhibit a subset of PPARgamma coactivators will be determined. As PPARgamma is acetylated and the cyclin D1 HDAC recruitment domain governs PPARgamma repression, the role of PPARgamma acetylation in repression by cyclin D1 will be determined. 2. Determine the mechanisms by which cyclin D1 inhibits PPARgamma function and expression. Cyclin D1 blocks PPARgamma induced differentiation of fibroblasts to adipocytes. We will identify the domain of cyclin D1 regulating PPARgamma differentiation. Cyclin D1 regulation of PPARgamma will be assessed in CD-/- mice, cyclin E knockin-CD-/- mice and in ponasterone-inducible cyclin D1 anti-sense mice. Correlative expression studies of PPARgamma and cyclin D1 will be conducted in 'benign' breast disease and breast cancers. 3. Determine the role of PPARgamma as a tumor suppressor of ErbB2-induced mammary tumorigenesis. We will determine the functional interactions between ErbB2 and PPARgamma in cultured cells and in ponasterone-inducible mammary gland-targeted PPARgamma transgenic mice. The use of inducible transgenics will allow the determination of PPARgamma function during mammary tumor onset and progression. If PPARgamma is an inhibitor of ErbB2-induced tumorigenesis and PPARgamma tumor suppressor function involves cyclin D1 repression, these studies provide a rational basis for identifying agonists of this interaction for potential therapeutic applications. Moreover, if PPARgamma levels are decreased in precursor lesions of breast cancer, the studies of PPARgamma in benign breast disease may provide a predictor of breast cancer progression. The proposed studies therefore may have important translational implications.